Acoustical filtration method and apparatus for obtaining instrumental tones

ABSTRACT

Electrical signals containing a large number of high-frequency components from a tone generator are amplified and converted by a small loudspeaker into audible-tones, which are led through an acoustical horn disposed in an enclosure, said accoustical horn having a multiplex-resonance characteristic to a microphone at the throat of the horn thereby to be converted again into electrical signals, which are amplified and finally converted by a second loudspeaker into audible tones.

United States Patent [191 Kato [ Mar. 5, 1974 ACOUSTICAL FILTRATION METHOD AND APPARATUS FOR OBTAINING INSTRUMENTAL TONES [75] Inventor:

[73] Assignee: Nippon Gakki Seizo Kabushiki Kaisha, l-lamamatsu-shi, Japan [22] Filed: Aug; 30, 1971 21 Appl. No: 176,102

[30] Foreign Application Priority Data [58] Field of Search.. 179/1 J, 1 MP, 107 R, 1 M, 179/1 D; 84/1.24, DIG. R; 181/27 A, 27 D,

Hirukazu Kato, l-lamamat'su, Japan I 2/1971 Pavia .5. 84/].24 2,978,543 4/1961 Kennedy 179/] J 3,276,535 10/1966 Shaw 179/107 R 2,403,232 7/1946 Parisier.. 179/1 J 2,517,819 8/1950 Young 179/1 J 2,942,070 6/1960 Hammond 181/27 A 2,107,804 2/1938 Roux l H 179/1 J 3,174,578 3/1965 Kojima 181/27 R Primary Examinerl(athleen l-l. Claffy Assistant ExaminerJon Bradford Leaheey Attorney, Agent, or Firm-l-lolman & Stern [57] ABSTRACT Electrical signals containing a large nurnber of highfrequency componentsfrom a tone generator are amplified and converted by a small loudspeaker into audible-tones, which are led through an acoustical horn disposed in an enclosure, said accoustical horn having a multiplex-resonance characteristic to a microphone [56] References Cited at the throat of the horn thereby to be converted again into electrical signals, which are amplified and finally UNITED STATES PATENTS converted by a second loudspeaker into audible tones. 2,493,638 1/1950 Olson 179/1 J 2,580,439 1/1952 Kock 179/1 MF 9 Claims, 4 Drawing Figures TONE COLOR C l R C U I T 1 TONE GENERATOR PATENTED 5 7 F l G.

TONE-COLOR CIRCUIT\ k lo GENERATOR Box IOOHZ IOOOHZ ACOUSTICAL FILTRATION METHOD AND APPARATUS FOR OBTAINING INSTRUMENTAL TONES BACKGROUND OF THE INVENTION This invention relates generally to generation of sound having a particular tone color, and more particularly to a new and advanced acoustical filtering method and-apparatus therefor, in which electrical signals are converted once into sounds, which are filtered in an acoustical system, and the resulting filtered sounds are again converted into electrical signals to produce tone signals having particular tone colors.

Heretofore, it has been a common practice to electrically synthesize or filter tone signals thereby to obtain electrical signals having specific frequency components and then to cause these signals to be rendered audible as sound such as electronic musical instrument tones. By this method, however, since electrical signals are processed totally in a purely electrical manner, it is difficult to produce faithfully instrumental tones having intricate frequency characteristics, especially wind instrument tones wherein the levels of the components of various frequencies vary intricately, whereby the resulting tones have had the disadvantage of lacking naturalness.

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the above described deficiency by providing an acoustical filtering method and apparatus wherein tone-source signals are acoustically filtered by passing them through an acoustical filtration system and are then converted into electrical signals.

According to this invention, briefly summarized,

, there are provided a method and apparatus for acoustical filtration wherein signals containing a large number of high-frequency components from a tone generator are once converted into audible tones, which are directed into and led through an acoustical horn disposed in an enclosure and having a multiplex-resonance characteristic to a microphone at the throat of the horn thereby to be converted into electrical signals, which are then amplified and finally converted into audible tones.

The naturejprinciple, and utility of the invention will be more clearly apparent from the following detailed description with respect to an example of preferred embodiment of the invention when read in conjunction with the accompanyingdrawing.

BRIEF DESCRIPTION, OF THE DRAWING DETAILED DESCRIPTION OF PREFERRED INVENTIVE EMBODIMENT The example of apparatus illustrated in FIG. 1 for accomplishing acoustical filtration according to the invention comprises, essentially, a tone generatorcircuit 1, an amplifier 2, a small-diameter loudspeaker 3, a

funnel-shaped acoustical horn 4 for guiding sound from the loudspeaker 3 to its throat 4a, a microphone 5 installed at the throat 4a of the horn.4, a box structure 6 defining an enclosure (preferably of sound proof enclosure) for enclosing the loudspeaker 3, the horn 4, and the microphone, an amplifier 7 for amplifying electrical signals from the microphone 5, and a loudspeaker 8.

The tone generator circuit 1 produces output signals containing a large number of high-frequency components, especially periodic pulse signals, the frequency specturm of these signals having a distribution as indicated in FIG. 2(a), for example.

These signals are amplified by the amplifier 2 and produced as sound from the loudspeaker 3. This sound is collected by the acoustical horn 4, which is disposed in the vicinity of the loudspeaker 3 and has an entrance of large cross-sectional area, and thereby guided to the microphone 5.

The acoustical horn 4 has a large number of resonance frequencies and has a so-called multiplexresonance effect, whereby the acoustical signals from the loudspeaker 3 are transmitted to the entrance of the microphone 5 as they undergo repeated reflections at the inner wall surface of the horn 4 through various paths in accordance with the frequency components thereof. Accordingly, the frequency transmission characteristic of an acoustical signal transmitted through the horn 4 to the entrance of the microphone is complex as indicated in FIG. 2'(b).

For this reason, by adjusting the output electrical signal of the microphone 5 to a suitable level, amplifying the same by means of the amplifier 7, and producing the same as an audible tone from the loudspeaker 8, an output tone having an intricate frequency spectrum characteristic as indicated in FIG. 2(c) is obtained. This output tone can be caused to acquire various characteristics by varying the resonance frequencies of the acoustical horn 4. Variation of the resonance frequencies can be accomplished by varying the shape, length, and diameters of the acoustical horn and can be achieved also by providing a plurality of holes 1 1 in the wall of the horn and changing the positions and numbers of these holes. I

The acoustical horn 4 may be of any shape provided that it has a large opening area on the side facing the loudspeaker 3, and the corss sectional area progressively decreases toward the throat 4a.

It should be understood, of course, that the foregoing disclosure relates to only a preferred embodiment of this invention and that it is intended to cover all changes and modifications of the example of the invention herein chosen for the purposes of the disclosure, which do not constitute departure from the spirit and scope of the invention.

For example, by passing the output of the tone generator circuit 1 through a separate tone-color circuit 10 which may comprise for instance a suitable filter known in electronic musical instruments and mixing the output of the type color circuit 0 to at a suitable level with the outputof the microphone 5, it is possible to produce tones of even more intricate characteristics.

In some cases, an electrical filter 9 may be inserted on the output side of the microphone 5.

The variation of the characteristics of the acoustical horn 4 can also be accomplished during rendition of the desired sounds, for example, by closing specific amplifiers 2 and 7 and adapted to be selectively used.

Thus, by the organization of the acoustical'filtration apparatus according to this invention as described above, musical tones possessing intricate frequency characteristics can be obtained in a simple manner, and the musical tones obtained, moreover, are rich in naturalness and faithful in reproduction.

1. An acoustical filtration method for obtaining instrumental tones having intricate selective frequency characteristics from a first set of electrical tone signals generated by a tone signal generator, comprising: converting said first set of signals into audible tones in an enclosure; directing and transmitting said audible tones within said enclosure into an acoustical horn featuring a plurality of selectable resonance frequencies and formed to have physical characteristics including a large cross sectional area at a mouth portion thereof and a narrow cross section of progressively decreasing area towards a throat region away from the mouth portion; selecting said plurality of resonance frequencies of said acoustical horn by varying the physical characteristics of theacoustical horn; converting such audible tones as are received by the horn within the enclosure into a second set or electrical signals by a microphonetransducer in the throat region; and rendering said second set of signals into acoustic output to obtain instrumental tones having intricate selective frequency characteristics.

2. A method asin claim 1 which includes a step of amplifying the first set of electrical tone signals prior to conversion thereof into audible tones in the enclosure.

3. A method as in' claim 1 which includes a step of fil tering said second set of electrical signals prior to said step of rendering the second set of signals into acoustic output.

4. A method as in claim 1 which includes the steps of diverting and passing a part of the first set of electrical tone signals through a tone-coloring circuit to obtain an auxiliary output, and mixing the auxiliary output with the second set of electrical signals resulting in instrumental tones having tone colored selective frequency characteristics. 1

5. An acoustical filtration apparatus for obtaining instrumental tones having intricate selective frequency instrument tones.

characteristics from tone signals containing a large number of high frequency components generated by a tone signal generator, comprising: a first loud-speaker disposed in an enclosure and connected to receive tone signals from the tone signal generator and convert them into a first set of audible tones; an acoustical horn disposed facing said first loudspeaker in said enclosure and formed to have a large cross sectional area at a I mouth portion thereof and a narrow cross section of progressively decreasing area towards a throat region away from the mouth portion, said acoustical horn having acoustical characteristics different from those of said first loudspeaker and featuring a plurality of selectable resonance frequencies; a microphone transducer disposed at said throat region for converting the plurality of selected resonance frequencies received thereby from the first loudspeaker into a second set of electrical signals, and a second loudspeaker for converting the second set of electrical signals into audible instrumental tone having intricate selected frequency characteristics.

6. An acoustical filtration apparatus according to claim 5 in which a first amplifier is connected between thetone signal generator and the'first loudspeaker to amplify the tone signals prior to their being renderedinto the first set of audible tones, and a second amplifier is connected between the microphone transducer and the second loudspeaker to amplify the second set of electrical signals prior to their being rendered into the audible instrumental tones.

7. An acoustical filtration apparatus according to claim 6 in which a tone-color circuit is connected between a junction point of the tone generator and the first amplifier and the junction point of the microphone transducer and the second amplifier thereby to mix an output of the tone-color circuit with thesecond' set of electrical signals. I

8. An acoustical filtration apparatus according to claim 5 in which an electricalfilter is connected to the output side of the microphone transducer to accom-. plish electrical filtration of the second set of electrical signals prior to their being converted into the audible 9. An acoustical filtration apparatus as in claim 5 which includes means to alter said plurality of selectable frequenciesso as to obtain required resonancefre- 

1. An acoustical filtration method for obtaining instrumental tones having intricate selective frequency characteristics from a first set of electrical tone signals generated by a tone signal generator, comprising: converting said first set of signals into audible tones in an enclosure; directing and transmitting said audible tones within said enclosure into an acoustical horn featuring a plurality of selectable resonance frequencies and formed to have physical characteristics including a large cross sectional area at a mouth portion thereof and a narrow cross section of progressively decreasing area towards a throat region away from the mouth portion; selecting said plurality of resonance frequencies of said acoustical horn by varying the physical characteristics of the acoustical horn; converting such audible tones as are received by the horn within the enclosure into a second set or electrical signals by a microphonetransducer in the throat region; and rendering said second set of signals into acoustic output to obtain instrumental tones having intricate selective frequency characteristics.
 2. A method as in claim 1 which includes a step of amplifying the first set of electrical tone signals prior to conversion thereof into audible tones in the enclosure.
 3. A method as in claim 1 which includes a step of filtering said second set of electrical signals prior to said step of rendering the second set of signals into acoustic output.
 4. A method as in claim 1 which includes the steps of diverting and passing a part of the first set of electrical tone signals through a tone-coloring circuit to obtain an auxiliary output, and mixing the auxiliary output with the second set of electrical signals resulting in instrumental tones having tone colored selective frequency characteristics.
 5. An acoustical filtration apparatus for obtaining instrumental tones having intricate selective frequency characteristics from tone signals containing a large number of high frequency components generated by a tone signal generator, comprising: a first loud-speaker disposed in an enclosure and connected to receive tone signals from the tone signal generator and convert them into a first set of audible tones; an acoustical horn disposed facing said first loudspeaker in said enclosure and formed to have a large cross sectional area at a mouth portion thereof and a narrow cross section of progressively decreasing area towards a throat region away from the mouth portion, said acoustical horn having acoustical characteristics different from those of said first loudspeaker and featuring a plurality of selectable resonance frequencies; a microphone transducer disposed at said throat region for converting the plurality of selected resonance frequencies received thereby from the first loudspeaker into a second set of electrical signals, and a second loudspeaker for converting the second set of electrical signals into audible instrumental tone having intricate selected frequency characteristics.
 6. An acoustical filtration apparatus according to claim 5 in which a first amplifier is connected between the tone signal generator and the first loudspeaker to amplify the tone signals prior to their being rendered into the first set of audible tones, and a second amplifier is connected between the microphone transducer and the second loudspeaker to amplify the second set of electrical signals prior to their being rendered into the audible instrumental tones.
 7. An acoustical filtration apparatus according to claim 6 in which a tone-color circuit is connected between a junction point of the tone generator and the first amplifier and the junction point of the microphone transducer and the second amplifier thereby to mix an output of the toNe-color circuit with the second set of electrical signals.
 8. An acoustical filtration apparatus according to claim 5 in which an electrical filter is connected to the output side of the microphone transducer to accomplish electrical filtration of the second set of electrical signals prior to their being converted into the audible instrument tones.
 9. An acoustical filtration apparatus as in claim 5 which includes means to alter said plurality of selectable frequencies so as to obtain required resonance frequencies. 